Problem: $\sin(-2\pi) = \text{?}$
Answer: To find the sine using the unit circle, first find the angle. Drag the orange point around the circle until $-2\pi$ is selected. The correct angle is selected. Remember, the sine of an angle is represented by the $y$ coordinate of a point on the unit circle. The $y$ coordinate of the point is $0$, so $\sin(-2\pi) = 0$.